1. Field of the Invention
This invention relates to a process for producing a belt-shaped member such as an intermediate transfer belt or a transfer material transport belt, used for electrophotography, and also relates to a belt-shaped transfer member produced by the production process, and an image-forming apparatus using the belt-shaped transfer member.
2. Related
Compared with an image-forming apparatus in which toner images are transferred from a first image bearing member (latent image bearing member) to a transfer material (such as paper) fastened or attracted onto a transfer drum (Japanese Application Laid-open No. 63-301960), an image-forming apparatus making use of intermediate transfer belts has such an advantage that a variety of transfer materials can be selected without regard to their width and length, including thin paper (40 g/m2 paper) and thick paper (up to 200 g/m2 paper) such as envelopes, post cards and labels.
Such an image-forming apparatus can also dramatically be improved in printing speed by using the first image-bearing member, a charging means, a developing means and so forth for each color developer and also using the intermediate transfer belt and the transfer material transport belt which attracts and transports transfer materials.
Full-color copying machines and printers making use of such a belt-shaped transfer member have various advantages as stated above. On the other hand, they also have some aspects for improvement.
As one of them, belt-shaped transfer members are necessarily large in size and also required to have various properties such as electrical resistance and surface properties, tending to result in high production costs. With regard to durability, too, some are not necessarily satisfactory and tend to have to be frequently changed for new ones. As a result, this may raise the main-body price and running costs of copying machines and printers and also it may take more labor and time for their maintenance. In particular, because of marketing trends in recent years, it has increasingly become important to achieve a lower price and provide maintenance-free articles.
In order to form good color images, some other problems must also be solved which may occur because a plurality of different colors are superimposed on the belt-shaped transfer member.
One of them is misregistration which may occur between individual colors. In fine lines and character images, even slight color misregistration tends to be conspicuous to provide a possibility of damaging image quality. When the belt-shaped transfer member is used, it must be put over a plurality of shafts, where the tension applied to every part of the transfer member is not necessarily uniform when driven and rotated. Hence, the belt-shaped transfer member tends to undergo local elongation and, concurrently therewith, may cause delicately uneven rotation. As a result, delicate color misregistration may appear when colors are superimposed, as so presumed.
Another problem is occurrence of spots around line images. This problem may seriously occur in image-forming apparatus in which toner images of different colors are superimposed on an intermediate transfer member and then collectively transferred to a transfer material. Superimposing different color toners enlarges the quantity of developer per unit area than in the case of monochromatic images. Especially in characters and fine lines, toners are present in a large quantity on narrow lines. Moreover, individual color toners have electric charges with the same polarity, and hence they are electrostatically repulsive to each other. Thus, it can be said that the toners are on the intermediate transfer belt in an unstable state.
Meanwhile, because of a difference in arcs drawn by the outer surface and inner surface of the intermediate transfer belt, produced when it passes through each shaft over which it is put, the intermediate transfer belt is elongated in the peripheral direction at its surface and in the vicinity thereof. Hence, the toner images standing unstable and weak to external disturbance as stated above are disordered because of such surface elongation of the intermediate transfer belt when it passes through the shafts, so that the spots around line images come to occur, as so presumed.
Still another problem is transfer performance of halftone toner images. Faulty images tend to occur when the belt-shaped transfer member has any uneven electrical resistance or uneven wall thickness.
Thus, there is room for further studies in order to obtain images with higher image quality. For the achievement of cost reduction, materials constituting the belt-shaped transfer member must be reduced in quantity to make them thin-gauge, and also a production process having a smaller number of steps must be provided. Making the belt thin-gauge also has the effect on prevention of the spots around line images caused by transfer, and is an effective means, but on the other hand the belt-shaped transfer member tends to be more elongated and also to raise a problem regarding durability.
Various processes for producing belts and tubes used for intermediate transfer members and so forth are already known in the art. For example, Japanese Patent Application Laid-Open No. 3-89357 and No. 5-345368 disclose a process for producing a semiconducting belt by extrusion. Japanese Patent Application Laid-open No. 5-269849 also discloses a process in which a belt is obtained by joining both ends of a sheet to bring it into a cylindrical form. Japanese Patent Application Laid-open No. 9-269674 discloses a process in which a belt is obtained by forming a multi-layer coating film on a cylindrical substrate and finally removing the substrate. Japanese Patent Application Laid-open No. 5-77252 discloses a seamless belt obtained by centrifugal molding.
The above processes each have merits and demerits. For example, in the extrusion, setting the die gap of an extruder die in the same size as the desired belt thickness involves considerable difficulties for producing thin-layer belts that can achieve the cost reduction and can control the occurrence of the spots around line images, tending to cause uneven wall thickness and uneven electrical resistance affected by such thickness. In the case where both ends of a sheet are joined, the difference in height and decrease in tensile strength at the joint presents problems. Still also, processes making use of solvents as in cast molding, coating and centrifugal molding require many steps of preparing and applying a coating solution, and removing the solvent, resulting in a high cost.
Accordingly, the present inventors propose a novel belt-shaped transfer member that is different from any conventional ones, having solved the above problems.
More specifically, an object of the present invention is to provide a process for producing a belt-shaped transfer member at a lower cost, in a smaller number of steps and in a rich variety of forms, and also provide a belt-shaped transfer member obtained by such a production process, and an image-forming apparatus having the belt-shaped transfer member.
Another object of the present invention is to provide a process for producing a belt-shaped transfer member which can contribute to the formation of good color images having less color misregistration and less spots around line images, and also provide a belt-shaped transfer member obtained by such a production process, and an image-forming apparatus having the belt-shaped transfer member.
Still another object of the present invention is to provide a process for producing a belt-shaped transfer member which can be free of any changes in its characteristics and can maintain characteristics at the same level as those at the initial stage, and also provide a belt-shaped transfer member obtained by such a production process, and an image-forming apparatus having the belt-shaped transfer member.
The present invention provides a process for producing a belt-shaped member usable as a transfer member (sometimes referred to herein as a xe2x80x9cbelt-shaped transfer memberxe2x80x9d) in an image-forming apparatus in which a visible image formed by developing with a developer an electrostatic latent image formed on a latent-image-bearing member is electrostatically transferred under application of a voltage via the belt-shaped transfer member; the process comprising the steps of;
melt-extruding a material containing a thermoplastic resin, from a circular die into a cylindrical film;
forming the resultant cylindrical film by stretching in such a way that the cylindrical film comes to have a thickness smaller than the die gap of the circular die; and
cutting the cylindrical film thus formed, into a seamless belt having a thickness of from 40 xcexcm to 300 xcexcm and a modulus in tension of 600 MPa or higher.
The present invention also provides a belt-shaped member usable as a transfer member in an image-forming apparatus in which a visible image formed by developing with a developer an electrostatic latent image formed on a latent-image-bearing member is electrostatically transferred under application of a voltage via the belt-shaped transfer member; the belt-shaped transfer member comprising a seamless belt having a thickness in a range of 40 xcexcm to 300 xcexcm and a modulus in tension of 600 MPa or higher, which is produced by;
melt-extruding a material containing a thermoplastic resin, from a circular die into a cylindrical film;
forming the resultant cylindrical film by stretching in such a way that the cylindrical film comes to have a thickness smaller than the die gap of the circular die; and
cutting into the seamless belt the cylindrical film thus formed.
The present invention still also provides an image-forming apparatus having the above belt-shaped transfer member.